1. Field of the Invention
The present invention relates to improved forms of moulded polymeric plastic material nursery trays and also to methods of manufacturing same.
2. Description of the Relevant Art
Traditionally nursery trays have been made from three types of construction. The first is from polystyrene foam, which due to the soft nature of the material has had very limited use in automatic transplanting machines. A second type of construction has utilised vacuum forming techniques whereby a pre-heated single sheet of plastic is formed with vacuum into a tray.
The nature of the previous methods of manufacture and shapes achievable from the pre-heated flat sheet were generally configured in a series of cells and interconnected by a flat upper surface which is sometimes formed downwardly around the outer perimeter for a short distance and then blanked out with a steel rule die to form an outwardly protruding thin flange. Generally, these are not very accurate for location or distance because of the flimsy nature of the vacuum formed tray and existing designs to date have not been suitable for automatic transplanting.
Injection die moulded hard plastic trays form a third form of construction and have been able to be manufactured in complex shapes and sizes and by the nature of being moulded by fluid plastic injected into chilled dies. Material section thickness and shapes are readily obtainable to enable the trays to be used in automatic transplanting machines, but by the nature of the complexity and cost of dies and the high capital costs of the moulding machines the relatively slow cycle time causing the costs to be such that the tray must be of a structure and design giving very long life and repeated usage which requires arduous cleaning and sterilising processes between nursery usages.
It is an object of this invention to enable the usage of a very lightweight, low cost vacuum formed tray to be used in automatic transplanting machinery, thereby providing precision plant placement with low labour cost. The invention preferably allows for a tray to be used effectively but because of its low cost, the tray may be used only once saving return freight from point of supply, maintaining absolute hygiene at the nursery and preventing any introduction of disease by way of returning trays and very importantly the invention provides for the ecologically friendly ability of the used tray to be recycled.
It is a further preferred objective to provide a nursery tray capable of use with automatic transplanting machinery of the type disclosed in Australian Patent Application No. 53040/98 or U.S. patent application Ser. No. 331,906, which specification is incorporated herein by this reference thereto.
The present invention provides an indexable vacuum formed nursery tray made from a sheet of polymeric plastic material having at least two aligned rows of indexing apertures formed in said sheet and a plurality of vacuum formed cells located between said rows of indexing apertures adapted to be filled with growing medium for plant propagation. Preferably, the sheet of plastic material is preformed with zones of thicker plastic material with said indexing apertures being formed in a said zone of thicker plastic material prior to vacuum forming of said cells. Preferably the sheet of plastic material is formed via an extrusion process which also includes providing at least some of said zones of thicker plastic material during the extrusion process.
Conveniently, the present invention also provides a nursery tray as aforesaid further including transverse stiffening ribs of relatively thicker plastic material between at least some adjacent rows of said cells, said stiffening ribs being disposed generally laterally relative to the rows of indexing apertures.
In accordance with one preferred nursery tray arrangement, a first said row of indexing apertures is provided on a first laterally extending flange portion on one peripheral side of the cells and a second said row of indexing apertures is provided on a second laterally extending flange portion on the other peripheral side of the cells, the nursery tray arrangement further having a depending stiffening flange portion extending downwardly from an outer edge of each of said first and second flanges towards a base region of the nursery tray arrangement. Preferably, the nursery tray arrangement further includes external or peripheral stiffening flange portions extending perpendicular to the stiffening flange portions located outwardly of the indexing apertures, the further stiffening flange portions being located at a peripheral edge of the outermost cells.
In accordance with another preferred nursery tray arrangement, a first said row of indexing apertures is provided in a bridging plastic material zone between adjacent said cells, and a second row of indexing apertures is provided spaced from said first row also located in a bridging plastic material zone between adjacent said cells. Multiple aligned said rows of indexing apertures may also be provide between the bridging plastic material zones between adjacent said cells, the number of said rows of indexing apertures being any number more than two up to and including all of the bridging plastic material zones between adjacent cells. The indexing apertures are conveniently preformed prior to vacuum forming the cells. The shape and positioning of the indexing apertures may be such as to cooperate with similarly formed indexing wheel teeth on an indexing mechanism. The apertures may be square, rectangular, circular or any other convenient shape.
In one particularly preferred nursery tray arrangement, a transversely formed trough is formed in at least one bridging plastic material region between adjacent rows of said cells, said trough or troughs extending substantially across said nursery tray laterally relative to said aligned rows of indexing apertures. Conveniently the trough or troughs are formed at the same time as the said cells, conveniently also by vacuum forming techniques.
The present invention also provides a method of forming a nursery tray having an array of propagating cells with at least two aligned rows of indexing apertures in spaced defined zones, said method involving the steps of:
(i) providing a sheet of plastic material capable of being formed;
(ii) forming said indexing apertures in said defined zones of said sheet;
(iii) restraining at least said defined zones to maintain a predetermined thickness of material in said defined zones; and
(iv) heating at least the remainder of said sheet and forming same to form said propagating cells without substantially reducing the thickness of said defined zones.
Preferably the sheet of plastic material may include thickened regions in a predefined pattern relative to the remainder of said sheet of plastic material, said predefined pattern at least including said spaced defined zones. Advantageously, the predefined pattern also includes regions intended to form stiffening ribs or formations in the tray.
In accordance with a still further aspect, the present invention provides an indexing and plant eject arrangement for use with nursery trays of the type including a plurality of cells arranged in predefined adjacent rows and at least two spaced aligned rows of indexing apertures generally perpendicular to said rows of cells, said arrangement including a guide means for guiding said trays along a substantially vertical path downwardly past an eject mechanism, said guide means including edge restraining means to restrain lateral edge regions of the trays during said downward movement, and a carrier mechanism moveable between a first position adopted to receive a plurality of seedlings or plants ejected from a said nursery tray and at least one second position adapted-to discharge one or more seedlings from the carrier mechanism, said carrier mechanism in said first position being adapted to engage said tray to at least restrain movement of said tray forwardly or transversely of said path during transfer by said eject mechanism of seedlings or plants from said tray to said carrier mechanism.
Conveniently, at least two spaced indexing wheels are provided having indexing teeth adapted to engage said indexing apertures from an underneath side of said trays.
Preferably the arrangement may include one or more upright guide members adapted to be received between adjacent cells as the tray is indexed in a downward direction, the guide member or members engaging an underneath side of the tray. Preferably, a cross guide support means is also provided to restrain forward movement of the tray or portions of the tray during indexing and/or ejection stages.
Preferred aspects of this invention allow for the use of extruded plastic sheet material either in a parallel flat form or with strategic ribbons of thicker section linearly along the extruded sheet. The thicker area of extrusion to be appropriately positioned to add stiffness and strength to the area in contact with the tray indexing mechanism.
In one preferred aspect, the invention provides for the unique forming of the shape of the upper surface of the tray that is interconnected to the cells positioned to be filled with growing medium for plant propagation. The unique features of the upper surface and sides of the tray which include preformed engaging teeth and/or sprocket gear engaging apertures to very accurately contain and control the stepped/indexed decent of the lightweight thin sectioned tray at very high speeds.
Similarly, in a still further preferred aspect, the present invention provides for the interaction of mechanical means to prevent deflection, distortion and misplacement during both the indexing phase and the ejection of plants and plugs. The invention also provides for provision to enable the lightweight vacuum formed tray to withstand the inertial shock loads caused by the sudden indexing for each row of cells to the next imposed on the trays when loaded with wet growing medium and live growing plants.
The claims as annexed hereto define the invention and further form part of the disclosure of the present specification.